1. Field of the Invention
The present invention relates to a lock-off mechanism for a switch and in particular, to a lock-off mechanism for selectively locking the power switch on a power tool.
2. Description of the Related Art
Within the field of power tools it is desirable to prevent accidental activation of such a tool before the user wishes to do so. In the working environment it is conceivable that the conventional trigger switches used in such power tools may be accidentally activated and start operation of the power tool before the operator so desires, which in the case of cordless power tools can drain the power source without the operator achieving their objective. Such trigger switches may be activated accidentally when the operator picks the tool up and unwittingly grasps the trigger switch, or should the power tool be left unattended it may be knocked or dropped on the floor to again activate the switch. This problem may be further exaggerated in such power tools having a click-on click-off mechanism whereby once a tool is switched on it must be positively switched off.
Attempts have been made to overcome this problem in the past whereby the trigger switch of the power tool will have an associated lock-off mechanism, having a button projecting outwardly through the body of the power tool in the region of the trigger switch and which internal of the tool positively engages the trigger switch to prevent it being accidentally depressed. For the user to then utilise the tool this button must be pressed inwardly to disengage it from the trigger switch to then allow the operator to depress to the trigger switch when required. However, drawbacks of such conventional trigger switch locking mechanisms includes the awkward positioning of such a button whereby if the operator were to try and utilise the tool one-handed he would lose grip on the power tool by having to use an extra digit to first depress the button before using the trigger switch, or to alternatively use two hands, one of which to depress the button, the second of which to grip the tool and depress the trigger switch. In the case where power tools require to be held steady during operation e.g. a drill or reciprocating saw, this has the drawback of the operator losing stability of the tool when first switched on since the hand usually used to stabilise the tool will be required to de-activate the lock-off mechanism.
An alternative example of a lock-off mechanism is disclosed in UK Patent Application No. 9718305.7.
It is therefore an object of the present invention to provide a lock-off mechanism for a switch which alleviates the aforementioned problems to allow improved utilage of such a power tool.